USB 6008 AI Input Circuit Explanation

[MattTurner]

On Page 12 of the NI USB-6008/6009 User Guide there is a Figure 7. that describes the USB-6008/600 Analog Input Circuitry (see figure below).

I'm struggling to understand the function of the resistor divider and series input resistor.  Current limiting and biasing circuit?  I would greatly explain an explanation of the circuit and the rationale for the resistor values.

MT